The invention relates to an optical apparatus for correcting the spherical aberration of a spherical concave mirror.
Whereas parabolic mirrors provide an absolutely parallel light beam when a punctiform light source is arranged in their focus, in the case of spherical concave mirrors parallelism to the optical axis can only be assumed in the case of light rays close to the axis. In the case of abaxial rays, the parallelism error increases with the distance from the optical axis. As spherical concave mirrors can be manufactured much more economically and accurately than parabolic mirrors, particularly above particular size limits, attempts have been made to eliminate by optical correction elements the parallelism error of a spherical concave mirror, which is also called the spherical abberation. The Schmidt correction plate and the Mangin mirror proposed for this purpose have the disadvantage that their manufacture, particularly when fulfilling the necessary high precision requirements is very expensive.